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  #1  
Old 08-30-1999, 06:42 AM
bdrought's Avatar
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Join Date: Apr 1999
Location: Milton Keynes, UK
Posts: 403
OK, I have a VERY slightly lumpy idle (my engine mounts are also shot which
makes it hard to feel the shudder) on my 91 300CE with 12V M103.

I've read that placing a 470ohm resistor inline with the coolant temp sensor can often alleviate this problem.

I dont want to put such a high value resistor in there.. I have some 200ohms
lying around that I was going to use.

Anyway, I pulled off what I thought was the temp sensor (upright large
plug - about spark plug sized - 4 pins) unplugged it, and snipped the jacket
away... Now, Which wires do I want to splice the resistor into? It has *4*
wires.

I presume one set is the engine management set and the other set is the dash
gauge set. Anyone know which is which????

Also, in drive or reverse with my foot on the brakes, there seems to be an
intermitant *bang* thru the brake pedal mostly. Could this be the fact the
engine is missing (it seems to idle at 500rpm in gear)

Is there something that tell the engine to increase speed when you select
gear? Where is it and how can I check it?

Sorry for all the questions folks, but I want to get my 'toy' working
properly, and also make sure nothing is getting damaged while its running
rough.

Oh...it starts hard aswell (joy!!)

Thanks,

Brian


------------------
Brian Drought
1991 300CE
http://www.users.globalnet.co.uk/~drought/
ICQ: 2180069
  #2  
Old 08-30-1999, 04:32 PM
Chris C.
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Well according to Geo. Murphy the last sensor on the head is the one you want, and the wire color is green w/ red tracer also I would stick w/ the 470 resistor as this is what is suggested.
I have not done this "upgrade" so your on your own.
BTW I also understand there has been an upgrade with the fuel pump relay giving a little richer idle, at warmer temps?
My 86' 300E had same type of problems, a new O2 sensor really straightened things out.
The clunk, maybe the bad mounts?
good luck,
Chris C.
  #3  
Old 08-30-1999, 11:29 PM
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Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
This mod was not for your car and Mercedes came out with a bulletin telling techs to take out the resistor when the idle modification was done. There is a mod for the 89 and older 103 engine cars where the 50 rpm drop when in gear is elliminated. Your car may have other problems such as bad engine mounts or fualty injectors, but I do not think there are any real mods for the 91.

------------------
Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM


  #4  
Old 08-31-1999, 04:16 AM
bdrought's Avatar
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Location: Milton Keynes, UK
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Would the fact that its a euro 103 make a difference?

It seems to drop around 100rpm in gear...

Thanks

Brian

------------------
Brian Drought
1991 300CE
http://www.users.globalnet.co.uk/~drought/
ICQ: 2180069
  #5  
Old 08-31-1999, 10:50 PM
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Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
It might. It depends on whether or not the car uses a mas relay or a regular fuel pump relay I think is the difference.

------------------
Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM


  #6  
Old 09-01-1999, 02:52 AM
bdrought's Avatar
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Join Date: Apr 1999
Location: Milton Keynes, UK
Posts: 403
Well........ I took it to a dealer, who diagnosed it as a shot distributor and a faulty wire end (I knew about the wire end).

Replaced these, and it runs better, starts better... vibration is still there, so it must be a mount.. I'll get it checked. Cheers.

------------------
Brian Drought
1991 300CE
http://www.users.globalnet.co.uk/~drought/
ICQ: 2180069
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